Differences in index arrays

My book mentions that I can delcare an array like this:

char line[5] = "Hello";

Or, like this:

char line[] = "Hello";

I understand the compilar will automatically pick out what number should be in the [] but does this take more memory? My book is strong on "Good coding ediket" (or something). Does it use less memory by telling the array the index #er? Or does it not matter?
Thanks in advance.

-andy

P.S. e-d-i-c-k-e-t is spelled wrong cause the forum picked up the word "d-i-c-k" in it. LOL!

char line[] = "hello"; will pick exactly the number of characters required to store the string (i.e.) 6 characters (5 characters + the trailing null character to delimit the string). It does not take more memory than is required. While you're at it:
char line[5] = "hello";
This should really read:
char line[6] = "hello";